Field of the Invention
The present invention relates to a robot system and a wiring method for a robot system, and in particular, to a robot system provided with a signal line enables a robot to stop in an emergency and a wiring method for a robot system provided with a signal line that enables a robot to stop in an emergency.
Related Art
To ensure the reliability of an emergency stop operation to stop a robot in the event of an emergency, a robot controller (referred to, hereafter, as simply a controller) may be provided with a plurality of systems of a means for performing the emergency stop operation by monitoring a safety input signal, such as an emergency stop signal or an enable signal. For example, JP-A-2011-88241 describes an invention in which a safety programmable logic controller (PLC) is provided within a controller.
In the case of robots for industrial use, a plurality of robots may be operated in an interlinked manner. In this case, each individual robot is controlled by a controller. Here, the controllers preferably start the emergency stop operation by a single safety input signal, that is, by operation of a single operating switch. A reason for this is that, when the plurality of robots are operated in an interlinked manner, if the other robots are in operation while one robot is stopped, for example, the position of a workpiece that is being gripped by two robots may become upset. In addition, a robot may come into contact with a worker who approaches the robot under an assumption that the robot has stopped, or a robot may come into contact with another robot that has already stopped, peripheral equipment, and the like.
Furthermore, when the plurality of robots are operated in an interlinked manner, the safety input signal is preferably inputted to all controllers. A reason for this is as follows. In the case of a configuration in which the safety input signal is inputted to a single controller that serves as a main controller and the other controllers are controlled as sub-controllers by the main controller, should malfunction occur in the main controller or an abnormality occur in the connection between the main controller and a sub-controller, giving an instruction to perform the emergency stop operation may no longer be possible.
Some controllers are provided with a function for detecting a failure on a path over which the safety input signal is inputted. The detection is made through determination of the certainty of the safety input signal. Specifically, the controller generates the safety input signal therein and outputs the generated safety input signal. The controller then determines whether or not a safety input signal that is inputted by way of an external operating switch matches the safety input signal outputted by the controller itself, in terms of cycle and pattern. Based on the determination, the controller detects a failure, such as a ground fault or a short circuit in the wiring. In this case, because the certainty of the inputted safety input signal is guaranteed, higher reliability can be ensured.
However, when a plurality of controllers such as that described above is present, when all controllers are connected to a single operating switch, as described above, a collision occurs among the safety input signals and normal monitoring cannot be performed. In this case, even should the safety input signal outputted from one controller also be connected to the other controllers, the inputted safety input signal is not a safety input signal that has been outputted from the other controllers in the first place. Consequently, the patterns do not match, and the other controllers determine the safety input signal to be abnormal. That said, should the function for confirming the certainty of the safety input signal be omitted, reliability will decrease.
In this way, when the plurality of systems of the means for performing an emergency stop operation by monitoring a safety input signal is provided, to enable each controller to perform the emergency stop operation in a state in which the certainty of the safety input signal is guaranteed, simple wiring that merely connects between controllers cannot be used.